The present invention relates generally to vacuum sewerage transport systems for conveying sewage collected in a holding sump to a downstream collection vessel maintained under the influence of vacuum or subatmospheric pressure, and more specifically to a differential pressure-operated controller mechanism for such a system that is free of externally mounted breather pipes, and is protected from waterlogging and hydrostatic pressure buildups.
Sewerage systems are commonly used to transport sewage and other waste liquids from a source, such as a residential or commercial establishment, to a collection vessel, whereupon the material is treated for subsequent disposal. The sewage is transported within an underground pipe network. Provided that the pipes can be laid in a continuous downhill slope, the sewage can be transported to the collection vessel by means of gravity. Often, however, one or more pumping stations are necessary to push the sewage by means of positive pressure through pipes elevated to avoid rocks, pipes, and other underground barriers, or to reduce the depth to which the pipes of a completely gravity-oriented system would need to be buried. In many instances, a positive pressure sewage system is used in which the pipes are laid largely without regard to topographical features, relying instead entirely upon pressure pumps located at every sewage input point to propel the sewage to the collection vessel.
Becoming increasingly popular are vacuum sewage systems, wherein sewage at atmospheric pressure is moved by means of differential pressure through a transport conduit maintained at vacuum or subatmospheric pressure by means of a vacuum pump operatively connected to the collection vessel. As shown more fully in FIG. 1, vacuum sewerage system 10 comprises a sump pit 12 buried beneath ground level 13 to which are connected a plurality of gravity lines 14 emanating from sewage sources 16. External gravity vent 18 positioned above ground ensures that sewage reaches sump pit 12 at atmospheric pressure.
Located above ground a distance away is a vacuum collection station containing a collection vessel 20 maintained at vacuum or subatmospheric pressure by means of vacuum pumps. Vacuum collection vessel 20 is operatively connected to sump pit 12 by means of a vacuum transport conduit 22. The vacuum transport conduit may be laid in a number of configurations. For example, it may be provided with "pockets" in which the sewage is collected so as to form a plug that entirely fills the cross-sectional bore of the conduit. The sewage plug is moved by means of differential pressure through the conduit in an integral condition. U.S. Pat. No. 3,115,148 issued to Liljendahl, and U.S. Pat. No. 3,730,884 issued to Burns et al. disclose such "plug-flow" systems. More preferably, the conduit portion leading to each pocket or low point is sloped such that the low point will not be filled with sewage upon completion of a sewage transport cycle, and an equalized vacuum or subatmospheric pressure condition is communicated instead throughout the conduit network. As taught by U.S. Pat. No. 4,179,371 issued to Foreman et al., a sewage/ air mixture in such a "two-phase flow" system is swept along the conduit during a transport cycle, so that the sewage can travel a greater distance than is possible with a plug-flow system.
A top panel 24 of sump pit 12 is connected to the sidewalls thereof in a sealed relationship in order to provide a pressure-tight vessel. Positioned on top of the top panel 24 is valve pit 26, which is accessed at ground level by a manhole cover 28. Located within valve pit 26 is vacuum interface valve 30. Examples of interface valves may be found in U.S. Pat. No. 4,171,853 issued to Cleaver et al., and U.S. Pat. Nos. 5,078,174 and 5,082,238 issued to Grooms et al, as well as U.S Ser. No. 07/829,742, now U.S. Pat. No. 5,259,427 07/967,454, now U.S. Pat. No. 5,326,069 and 08/008,190, now U.S. Pat. No. 5,282,281, owned by the assignee of the present invention. As shown generally in FIG. 2, it comprises a wye-body conduit 32 having an inlet 34 which is operatively connected to sump pit 12 by means of suction pipe 36, and an outlet 38, which is operatively connected to vacuum transport conduit 22. Positioned within valve housing 40 is plunger 42, which may be conically shaped. An elastomeric seat 44 is attached to one end of plunger 42, and cooperates with valve stop 46 of wye-body conduit 32 to regulate passage of sewage through interface valve 30. Secured to the top of valve housing 40 is lower housing 48 and upper housing 50, which are divided by means of elastomeric diaphragm 52. Lower housing 48 is always maintained at atmospheric pressure by means of externally mounted breather pipe 54 and atmospheric hose 56. Plunger 42 is connected to piston cup 58 by means of piston shaft 60, and a spring 62 positioned between the interior of piston cup 58 and the top of upper housing 50 biases valve seat 44 against valve stop 46 to close interface valve 30 when upper housing 50 is at atmospheric pressure. However, once upper housing 50 is switched to a vacuum or subatmospheric pressure condition, diaphragm 52--and consequently piston cup 58, piston shaft 60, plunger 42, and valve seat 44--is moved away from valve stop 46 by means of differential pressure to open interface valve 30 to commence a sewage transport cycle.
Sensor-controller 66 is used to deliver a vacuum/subatmospheric or atmospheric pressure condition to upper housing 50 so to open or close interface valve 30 in response to the sewage level in sump pit 12. The structure of sensor-controller 66 is described more fully in U.S. Pat. No. 4,373,838 issued to Foreman et al. As shown in FIGS. 3-4, however, the structure and mode of operation is generally as follows. A plurality of body elements 68, 70, 72, 74, and 76 cooperate to form hydrostatic pressure chamber 78, sensor chamber 79, chamber 80, chamber 81, vacuum chamber 82, and valve chamber 84. Chambers 78 and 79 are divided by means of elastomeric diaphragm 86. Chambers 79 and 80 communicate by means of port 88, which may be closed by spring biased lever valve 90 (see FIG. 3). Chambers 80 and 81 are divided by means of elastomeric diaphragm 92 to which is attached piston rod 94 that extends through chamber 81, chamber 82, and into chamber 84. Vacuum chamber 82 is maintained at vacuum or subatmospheric pressure by means of vacuum inlet port 96 and vacuum hose 98 which is attached to vacuum transport conduit 22. Surge tank 100 may be interposed in vacuum hose 98 to prevent sewage from entering vacuum chamber 82. Atmospheric inlet port 102 delivers atmospheric pressure to sensor-controller 66 by means of atmospheric hose 56 connected to external breather pipe 54. Atmospheric pressure, in turn, is delivered to sensor chamber 79 by means of inlet 104 and atmospheric conduit 106.
To the other end of piston rod 94 is connected three-way valve seat 108 made from a plastic material. Flange 110 on valve seat 108 is positioned between elastomeric seals 112 and 114 which communicate vacuum/subatmospheric and atmospheric pressure from vacuum chamber 82 and atmospheric inlet port 102, respectively, to valve chamber 84.
Sensor-controller 66 is shown in the closed position in FIG. 3. Hose 116 operatively connected to sensor pipe 37 communicates the hydrostatic pressure level in sump pit 12 to chamber 78 through inlet port 118. Meanwhile, sensor chamber 79 is at atmospheric pressure. The vacuum/subatmospheric pressure condition of vacuum chamber 82 is communicated to chambers 80 and 81 by means of vacuum conduit 120. Flange 110 of valve seat 108 closes vacuum vent 112, and opens atmospheric vent 114 to allow atmospheric pressure to pass into valve chamber 84, and therefore into upper valve housing 50 through pressure vent 122.
Once the hydrostatic pressure communicated to chamber 78 rises to a predetermined level, however, diaphragm 86 is biased into contact with lever valve 90, which in turn is activated to open port 88 so that the vacuum/subatmospheric pressure in chamber 80 is replaced with the atmospheric pressure condition of sensor chamber 79 (see FIG. 4). This creates a differential pressure across diaphragm 92, which pushes piston rod 94 so that valve flange 110 closes atmospheric vent 114 and opens vacuum vent 112, whereupon vacuum/subatmospheric pressure is delivered into vacuum chamber 84, and through pressure vent 122 into upper valve housing 50 to open interface valve 30 to commence a sewage transport cycle. Meanwhile, vacuum/subatmospheric pressure in vacuum chamber 82 is leaked through vacuum conduit 120 into chamber 80 to replace the atmosphere pressure therein, and once it reaches a sufficient level, the process is reversed to return sensor-controller 66 to once again closed position shown in FIG. 3 to terminate the sewage transport cycle.
It has been found, however, that the above-ground breather pipe 54 provides several disadvantages. First, unlike gravity vent 18 which may be conveniently positioned against building 16 in a secluded state, valve pit 26 is typically located out in a yard or field, so the associated breather pipe 54 cannot be so easily hidden, and therefore is aesthetically displeasing. Second, because of its open, unprotected position, above-ground breather pipe 54 may be subject to vandalism or damage by a lawn mower, car, etc. This disrupts the reliable supply of atmospheric pressure to sensor-controller 66 and interface valve 30 required for their proper operation.
Consequently, U.S. Pat. No. 4,691,731 issued to Grooms et al. teaches a sump/valve pit structure 130, as shown in FIG. 5, in which breather pipe 54 is eliminated, and instead, atmospheric pressure is supplied by sump pit 12. More specifically, sensor pipe 37 is secured to sump pit top panel 24 by means of a sleeve 132 and collar 134 assembly. Collar 134 has three nozzles 136, 138, and 140 extending therefrom (see FIG. 5a). Breather tube 142 is attached to nozzle 136 and atmospheric inlet port 102 of sensor-controller 66 (FIGS. 3 & 4), thereby allowing atmospheric pressure contained in sump pit 12 to be freely communicated to the sensor-controller. Vent tube 144, in turn, is attached to nozzle 138 and lower housing 48 of interface valve 30, thereby providing atmospheric pressure thereto. Finally, drainage tube 146 may be attached to lower housing 48 and nozzle 140, ensuring that any moisture that condenses within lower housing 48 may be easily drained back through sensor pipe 37 into sump pit 12. Under normal operating conditions, this "in pit breather" arrangement provides atmospheric pressure to sensor-controller 66 and interface valve 30 without above-ground breather pipe 54.
Problems arise, however, if the vacuum/subatmospheric pressure condition within vacuum transport conduit 22 diminishes to a low vacuum condition. Referring to FIGS. 3-4, once the hydrostatic pressure condition delivered to chamber 78 by sensor pipe 37 and pressure tube 116 reaches the predetermined level as sewage accumulates in sump pit 12, diaphragm 86 is biased to open lever valve 90, and chamber 80 is converted to atmospheric pressure (i.e., 0 vacuum), while chamber 81 is at low vacuum. The differential pressure across valve diaphragm 92 is too small to overcome the counterforce exerted by spring 95 to move piston rod 94 and valve head 108 sufficiently to completely close off atmospheric vent 114. Moreover, the low vacuum pressure passed through vacuum vent 112 and pressure vent 122 into upper housing 50 is insufficient to open interface valve 30. Not only can sewage not be evacuated from sump pit 12 through suction pipe 36 and closed interface valve 30 to vacuum transport conduit 22, but also sewage continues to collect in the sump.
Once the sewage level in sump pit 12 rises to a sufficient level, positive pressure therein pushes sewage through breather tube 142 to atmospheric inlet port 102 of sensor-controller 66. The atmospheric pressure in sensor valve chamber 79 will temporarily keep the sewage from entering it via atmospheric conduit 106. However, once lever valve 90 is opened when the sensor-controller valve is fired, atmospheric pressure leaks from sensor valve chamber 79 into chamber 80. Moreover, atmospheric pressure can leak from sensor valve chamber 79 through vacuum conduit 120, vacuum hose 98, and surge tank 100 into vacuum transport conduit 22. By reducing the atmospheric pressure condition in sensor valve chamber 79, sewage may now enter it and the rest of the sensor-controller chambers through the aforementioned paths to ensure that sensor-controller 66 cannot operate properly until it is manually drained by service personnel.
Thus, U.S. Pat. No. 4,691,731 also discloses a sump-vent valve which may be interposed within vacuum hose 98, and is closed by a low vacuum condition to prevent communication of the low vacuum to sensor-controller 66 which can cause atmospheric pressure in sensor valve chamber 79 to leak, and thereby compromise the sealed nature of chamber 79 that otherwise keeps sewage out of sensor-controller 66.
It has been found, however, that there are several problems that can seriously thwart the operation of sensor-controller 66 and interface valve 30 that are not rectified by the sump-vent valve. First, the sump-vent valve is initially set to close at the correct time once a low vacuum pressure condition arises. For example, if 5 inches of vacuum is required to operate sensor-controller 66, and the sump-vent valve is set to close at 6 inches of vacuum, then the system works. However, if over time the sump-vent valve begins to close at 41/2 inches of vacuum, then it is not activated soon enough as the vacuum pressure within the system 10 drops, and low vacuum can be communicated to sensor-controller 66 to allow sewage to enter it, despite the presence of the sump-vent valve.
Second, even if the sump-vent valve operates properly, once full vacuum is restored to the system, sensor-controller 66 will be activated to the open position in response to the elevated hydrostatic pressure condition already stored in chamber 78. Some atmospheric pressure will be consumed in the process, which will cause sewage to be pulled through breather tube 142 into sensor-controller 66.
Third, breather tube 142 is connected to the top of sensor pipe 37 that extends through sump pit top 24. If the seal between sleeve 132 and top 24 fails, then atmospheric pressure can leak out of sump pit 12 into valve pit 26. This permits even more sewage to collect in sump pit 12 if the low vacuum condition that renders sensor-controller 66 and interface valve 30 inoperative by the sump-vented valve persists over an extended period of time. Once full vacuum is restored, and sensor-controller 66 is activated, enough atmospheric pressure can leak within sensor-controller 66 to draw sewage into it, as previously described.
Another problem arises if gravity line 14 is installed improperly or settles over time to create a dip therein. If the cross-sectional bore of the dipped portion becomes filled with sewage, then atmospheric pressure from gravity vent pipe 18 cannot be communicated to sump pit 12 to be passed to sensor-controller 66 and interface valve 30. This could prevent the sensor-controller and interface valve from operating properly. Furthermore, if hydrostatic pressure builds sufficiently in sump pit 12, then it, and not atmospheric pressure, can be communicated to atmospheric inlet port 102 of sensor-controller 66. Thus, hydrostatic pressure would be communicated to both ends of sensor-controller 66, and then to chambers 78 and 79, which would render sensor-controller 66 completely inoperative.